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Plastic behavior of monoclinic polypropylene under hydrostatic pressure in compressive testing
Author(s) -
Staniek Eric,
Seguela Roland,
Escaig Bertrand,
François Philippe
Publication year - 1999
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/(sici)1097-4628(19990606)72:10<1241::aid-app2>3.0.co;2-w
Subject(s) - materials science , polypropylene , hydrostatic pressure , monoclinic crystal system , composite material , polyethylene , plasticity , ultimate tensile strength , thermodynamics , crystallography , chemistry , crystal structure , physics
The plastic deformation of monoclinic isotactic polypropylene is studied in compressive testing with particular attention to the effect of hydrostatic pressure up to 300 MPa, in the temperature range 20–60°C. The coefficients of the Coulomb criterion are fairly consistent with those assessed from the comparison of the tensile and compressive yield stresses at atmospheric pressure, in the same temperature range. The high friction coefficient of polypropylene is ascribed to a strain‐induced order‐to‐disorder transition from the monoclinic to the smectic form accompanied by an increase of specific volume. This local and transient phase change is assumed to result from the mobile conformational chain defects that govern the elementary mechanism of plasticity in the crystalline phase of polypropylene consisting of 3/1 helix chains. A comparative discussion is made with polyethylene that displays a much lower friction coefficient. The dislocation‐based approach that is proposed in relation to the viscoelastic relaxation processes provides a new insight into the molecular grounds of the elementary mechanism of plasticity of polypropylene. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1241–1247, 1999